The present invention relates to a melting and holding furnace for aluminum blocks, and more particularly to a melting and holding furnace comprising, as constituent elements, a pre-heating tower for pre-heating aluminum blocks and two crucible furnaces for melting and holding aluminum materials respectively. The term xe2x80x9caluminum blockxe2x80x9d used in the specification refers to aluminum ingots or like aluminum masses, collected aluminum-containing materials (empty cans of aluminum and other aluminum scraps) pressed into blocks in substantially the similar shape to aluminum ingots, and so on.
To melt and hold aluminum materials, various apparatus are known and include an apparatus wherein molten aluminum is transported and distributed by a ladle or the like from a centralized melting furnace to an electrically or otherwise heated individual furnace solely serving for holding purpose; an individual furnace provided for melting and holding purposes and housing a melting chamber and a holding chamber each having a receptacle constructed with refractory bricks and accommodating molten metal; a graphite crucible furnace; etc.
The graphite crucible furnace has a construction wherein a graphite crucible is provided in a cylindrically constructed furnace and the crucible is heated by a burner. For melting in the graphite crucible, metal ingots are charged directly from an upper portion of the crucible. If metal ingots are thrown into the crucible and positioned diagonally to contact the crucible sidewall, the ingots would be likely to push apart the sidewall due to thermal expansion. In view of this likelihood, metal ingots as longitudinally arranged are thrown into the crucible.
In melting aluminum materials in a conventional crucible furnace, aluminum ingots have been directly thrown into a crucible through an opening formed therein. Consequently, the melt of aluminum is cooled immediately thereafter, and the temperature of aluminum melt begins to arise after the aluminum ingots have been all melted. In this case, on reaching a specific temperature, the melt is drawn out for casting. When the amount of the melt decreases by bailing out the melt, aluminum ingots are supplied again. In this way, melting and bailing-out operations are alternately practiced and repeated batchwise in the crucible furnace. Consequently problems arise that a constant supply of the melt is not done, and that a small amount of aluminum ingots should be supplied to adjust the temperature of the melt. Further, aluminum materials such as aluminum ingots are supplied to the melt without being preheated so that the temperature of the melt is widely variable.
When a centralized melting furnace is used, a large amount of molten aluminum should be retained all the time. Moreover, the centralized melting furnace is difficult to use in melting aluminum blocks currently produced including a wide variety of materials. In addition, the temperature of the melt being distributed should be elevated to make up for the reduction in the temperature unavoidably caused by the distribution of the melt. In other words, such furnace is not suitable for diversified small-quantity production. Another problem is a difficulty entailed in control of production since a specific amount of the melt cannot be retained during the maintenance of the centralized melting furnace.
Moreover, in the case of using an integrated type melting and holding furnace having a melt receptacle lined with bricks or the like, the flame of the heating burner is directly applied to the melt. Said furnace raises problems such as contaminating the melt with an oxide or absorbing hydrogen gas, thereby affecting the quality of cast articles. The furnace is also defective in leading to a large amount of accumulated heat in the furnace wall, making it difficult to achieve energy savings and necessitating high maintenance costs and a period of time for the relining of the furnace wall with bricks at a regular time.
A main object of the present invention is to provide a melting and holding furnace for aluminum blocks which furnace is capable of overcoming all of the foregoing prior art problems, continuously melting aluminum materials and attaining energy savings.
To achieve the foregoing object, the present invention provides a melting and holding furnace for aluminum blocks, the furnace being characterized in that the furnace comprises:
a pre-heating tower for pre-heating aluminum blocks,
a melting crucible furnace which receives a supply of aluminum blocks from the pre-heating tower at a position immediately under the pre-heating tower, and
a holding crucible furnace which receives a continuous supply of molten aluminum from the melting crucible furnace at a position side-by-side with the melting crucible furnace, and
that exhaust gas resulting from combustion in the melting crucible furnace can be supplied to the inside of the pre-heating tower as an ascending current for heat exchange with aluminum blocks.
The melting and holding furnace of the present invention can achieve the following results.
(1) The furnace of the present invention can be used in melting not only aluminum blocks but a composite material comprising aluminum (or aluminum alloy) and other metals such as iron.
(2) The furnace of the present invention is a crucible-type melting and holding furnace capable of continuously melting metal.
(3) The furnace of the present invention can melt a metal at a specific low temperature in the vicinity of the melting point of aluminum, thereby giving numerous beneficial results that a less quantity of oxide, such as aluminum oxide, is generated and hydrogen gas is absorbed in a less amount, resulting in a high quality melt; the temperature in the holding crucible furnace can be easily controlled; and the service life of the crucible can be extended because of good conditions for the durability of the crucible.
(4) The pre-heating tower enables a great degree of energy savings, and the furnace of the invention shows a high melting capability relative to its furnace volume and is lightweight and compact.
(5) Since the crucible can be easily replaced, the furnace is suitable for melting diversified meterials.
(6) The stoppage of melting and the control of a melting rate can be adjusted only with the combustion gas, thereby facilitating the control of production.
(7) The furnace need not be repaired on a large scale with regular intervals, and maintenance can be easily performed at low costs only by replacement of crucibles.
(8) Working environment can be improved because of low-temperature exhaust gas.
Other features of the present invention become apparent from the following description with reference to the accompanying drawing.